Methods of producing cermet materials and methods of utilizing same

ABSTRACT

Methods of fabricating cermet materials and methods of utilizing the same such as in filtering particulate and gaseous pollutants from internal combustion engines having intermetallic and ceramic phases. The cermet material may be made from a transition metal aluminide phase and an alumina phase. The mixture may be pressed to form a green compact body and then heated in a nitrogen-containing atmosphere so as to melt aluminum particles and form the cermet. Filler materials may be added to increase the porosity or tailor the catalytic properties of the cermet material. Additionally, the cermet material may be reinforced with fibers or screens. The cermet material may also be formed so as to pass an electrical current therethrough to heat the material during use.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application is a Divisional of U.S. application Ser. No. 10/213,112entitled METHOD OF FABRICATING CERMET MATERIALS AND METHOD OF UTILIZINGSAME, filed on Aug. 5, 2002 now U.S. Pat. No. 7,022,647: Applicant NotesU.S. application Ser. No. 10/213,120 entitled CERMET MATERIALS,SELF-CLEANING CERMET FILTERS, APPARATUS AND SYSTEMS EMPLOYING SAME,filed on Nov. 4, 2002 claims priority to the above referenced U.S.application Ser. No. 10/213,112.

STATEMENT OF GOVERNMENT RIGHTS

The United States Government has certain rights in this inventionpursuant to Contract No. DE-AC07-99ID13727, and Contract No.DE-AC07-05ID14517 between the United States Department of Energy andBattelle Energy Alliance, LLC.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to cermet filters used to filter combustionproducts from internal combustion engines. More particularly, thisinvention relates to a porous, intermetallic-ceramic composite filterthat is self-cleaning and can improve emissions from internal combustionengines.

2. State of the Art

Emissions from vehicles, such as heavy-duty diesel engine vehicles,contribute greatly to pollution problems of the United States of America(USA). Heavy-duty vehicle emissions produce ozone, particulate materials(PM), nitrogen oxides (NO_(X)), sulfur oxides (SO_(X)), and volatileorganic compounds (VOCs). These emissions can cause adverse healtheffects such as premature mortality, aggravation of respiratory andcardiovascular disease, chronic bronchitis, changes to lung tissues andstructures, and altered respiratory defense mechanisms, among otherthings. Further, ozone is known to cause crop and forestry losses and PMcauses damage to materials and soiling. NO_(X) and PM also significantlycontribute to unsightly smog and substantial visibility impairment inmany parts of the USA.

Emissions from diesel engine heavy-duty trucks significantly contributeto these problems throughout the country. By 2007, heavy-duty vehicleswill account for 29 percent of NO_(X) and 14 percent of PM emissions inthe USA. These proportions are even higher in some urban areas. Forexample in Albuquerque, N. Mex., heavy-duty vehicles contribute 37percent of NO_(X) and 20 percent of PM emissions.

The United States Environmental Protection Agency (EPA) is proposing aPM emissions standard for new heavy-duty engines of 0.01 grams perbrake-horsepower-per hour (g/bhp-hr) to take full effect in 2007. TheEPA is also proposing more stringent standards for NO_(X) and VOCemissions to be phased in between 2007 and 2010. In order to meet theserigorous new standards, new and improved filters are needed.

Engine and catalyst manufacturers have experimented with many catalyticconverters and with a wide variety of regenerative catalytic traps.Precious metal catalytic traps are somewhat effective in oxidizinggaseous hydrocarbons and CO as well as the particulate soluble organicfraction (SOF). However, precious metal catalysts are very expensive.Base metal catalytic traps promote soot oxidation but have little effecton NO_(X), CO_(X), or SO_(X).

Intermetallic-ceramic catalyst supports have been produced in the past.For example, U.S. Pat. No. 5,951,791 to Bell et al. discloses usingnickel aluminide to coat the inside of an alumina fiber preform. U.S.Pat. No. 5,774,779 to Tuchinskiy and U.S. Pat. No. 4,990,181 to Pierottiet al. disclose using nickel aluminide as a catalyst support. U.S. Pat.No. 4,992,233 to Swaroop et al. discloses using iron aluminide alloys inexhaust filter applications. Also, U.S. Pat. No. 5,496,655 to Lessingdiscloses using a porous NiAl or Ni₃Al with a ceramic filler to catalyzesteam reforming of hydrocarbons to power fuel cells.

Porous ceramic filters made from carbide and oxide materials are wellknown in the art. However, conventional ceramic filters used withheavy-duty diesel engines have a significant lifetime problem. Theseceramic filters have a short lifetime due to severe carbon particulateplugging and structural failure due to high vehicle motion stresses andextreme thermal stresses. Typically, the filters are plugged after 500hours of service, which makes them a financial and operational liabilityfor companies. Further, the filters often require complicated heatingand control systems.

BRIEF SUMMARY OF THE INVENTION

The present invention fulfills the need in the art for a strong andtough porous intermetallic-ceramic composite filter that not onlyfilters particulates but reduces undesirable gaseous pollutants. Thepresent invention eliminates the need for complicated systems to heatthe filter and is self-cleaning so it does not plug up with particulatematter. Further, the intermetallic-ceramic composite filters of thepresent invention do not require coating with other materials forfunctioning.

The present invention comprises a self-cleaning filter used forfiltering particulate and gaseous pollutants from internal combustionengines. The filter is made from a porous cermet-type material having anintermetallic phase and a ceramic phase.

An exemplary embodiment uses a porous cermet filter having a transitionmetal aluminide phase such as cobalt, iron, nickel, or titanium-typealuminides and an alumina phase.

In another exemplary embodiment, a reinforcement material such as metalfibers, ceramic fibers, or metal screens may be incorporated into theporous cermet filter for added strength.

In another exemplary embodiment, the porous cermet filter iselectrically conductive and a current may be passed therethrough to heatit during use.

In another exemplary embodiment, at least one resistive heating elementmay be incorporated into the porous cermet filter during manufacture. Anelectrical current may be applied to the resistive heating element toheat the porous cermet filter during use.

In another exemplary embodiment, the resistive heating element has acoefficient of thermal expansion approximately the same as that of thecermet material.

In another exemplary embodiment, the resistive heating element may becoated with a ceramic material prior to incorporation into the cermetfilter.

In another exemplary embodiment, the ceramic material coating theresistive heating element electrically insulates it from the cermetmaterial.

In another exemplary embodiment, an external heating element may beprovided to heat the porous cermet filter during use.

In another exemplary embodiment, the cermet may be manufactured using acombustion synthesis process by forming a green compact of a transitionmetal, aluminum, and alumina particles to produce a transition metalaluminide-alumina porous cermet filter. Alternatively, aluminum andthermite particles may be used to produce a nickel aluminide-aluminaporous cermet filter.

In another exemplary embodiment, the combustion synthesis process may beperformed under a nitrogen-containing atmosphere to formammonia-producing phases in the porous cermet filter.

In another exemplary embodiment, the combustion synthesis process may beperformed with sugar added to the green compact under anitrogen-containing atmosphere to form ammonia-producing phases in theporous cermet filter.

In another exemplary embodiment, the combustion synthesis process may beperformed with an alkali carbonate or an alkali bicarbonate and sugaradded to the green compact under a nitrogen-containing atmosphere toform ammonia-producing phases and hydrocarbon gas-producing phases. Inthis embodiment, an alkali oxide is formed during the combustionsynthesis process, which may either be leached out to increase porosityor left in the cermet filter because of its ability to absorb NO_(X).

In another exemplary embodiment, a sacrificial filler may be added tothe green compact to increase the porosity of the cermet filter.

In another exemplary embodiment, a porous cermet filter may be producedwith a graded porosity by layering relatively larger and smallersacrificial filler materials in the green compact.

In another exemplary embodiment, electrodes may be incorporated into theporous cermet filter during the combustion synthesis process.

In another exemplary embodiment, a housing may be bonded to the porouscermet filter during the combustion synthesis process.

The disclosed invention also encompasses methods of manufacture and useof the inventive cermet filter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, which illustrate what is currently considered to be thebest mode for carrying out the invention:

FIG. 1 is sectional view of a porous cermet filter.

FIGS. 2A and 2B are photomicrographs of the microstructure of the cermetmaterial in FIG. 1.

FIG. 3A is a sectional view of a porous cermet filter produced withsugar filler materials.

FIG. 3B is a sectional view of a porous cermet filter produced withhuman hair sacrificial filler materials.

FIG. 3C is a longitudinal view of a porous cermet filter produced withhuman hair sacrificial filler materials.

FIG. 3D is a sectional view of a porous cermet filter having a gradedporosity.

FIGS. 3E and 3F are views of a porous cermet filter having a gradedporosity across the length thereof.

FIG. 4A is a longitudinal view of a porous cermet filter with areinforcement material.

FIG. 4B is a sectional view of a porous cermet filter with areinforcement material.

FIG. 4C is a sectional view of a porous cermet filter with multipleresistive heating elements.

FIGS. 5A and 5B are gas chromatography analyses of an activated cermetfilter produced by a combustion synthesis process under a nitrogenatmosphere.

FIGS. 6A and 6B are gas chromatography analyses of an activated cermetfilter produced by a combustion synthesis process using a sodiumbicarbonate and sugar filler material.

FIG. 7 is a view of electrodes bonded to a cermet filter.

FIG. 8A is a sectional view of a cermet filter having multiple resistiveheating elements.

FIG. 8B is a view of the cermet filter of FIG. 9A.

FIG. 8C is a sectional view of a resistive heating element coated with aceramic material.

FIG. 9 is a sectional view of a cermet filter with an external heatingelement.

FIGS. 10A and 10B are sectional views of a cermet filter bonded to afilter housing.

FIGS. 11A and 11B are flow diagrams showing a porous cermet filtercoupled to an exhaust system of an internal combustion engine from avehicle.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, a sectional view of filter 10 made from cermet 12and having pores 14 is shown. For purposes of illustration, the sizes ofpores 14 in relation to filter 10 are exaggerated. The porous structureof filter 10 is used for its high internal surface area in order to trapparticulate matter and for chemical reactions. In an exemplaryembodiment, pores 14 are irregular in shape and non-linear. In anotherexemplary embodiment, filter 10 may be disk or cylinder shaped. Cermet12 in filter 10 is a metallic-ceramic composite material. Cermet 12 offilter 10 may be coating free, in that it lacks a coating of anothermaterial deposited over the inside of pores 14.

Referring to the photomicrographs of FIGS. 2A and 2B, a representativemicrostructure of cermet 12 is shown having a ceramic phase 16 and ametallic phase 18. As shown in FIGS. 2A and 2B, ceramic phase 16 may bediscontinuous and bonded by metallic phase 18. FIG. 2A shows a 50 wt %NiAl-50 wt % alumina cermet 12 formed from fine alumina particlesapproximately 5-10 μm in size, nickel particles, and aluminum particles.FIG. 2B shows a 50 wt % NiAl-50 wt % alumina cermet 12 formed fromcoarse ceramic particles approximately 100-200 μm in size. Variousintermetallic compounds may be used for metallic phase 18, such asaluminide compounds of the form AB or A₃B. In an exemplary embodiment,the metallic phase 18 is an aluminide such as NiAl, Ni₃Al, FeAl, Fe₃Al,CoAl, CO₃Al, or other transition metal aluminides due to the desirablecatalytic properties of transition metals. Transition metals are definedas the elements Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn. Ceramic phase16 may be oxide or non-oxide ceramics. Exemplary materials for ceramicphase 16 include alumina (Al₂O₃), zirconia silicate (ZrSiO₄), zirconia,mullite, cordierite, or iron III oxide (Fe₂O₃). In an exemplaryembodiment, ceramic phase 16 may be a refractory material, allowingfilter 10 to be used at very high temperatures.

Depending on the intended use of filter 10, the composition of cermet 12may be tailored to affect certain functional characteristics such asincorporating specific catalysts to perform selected catalysis orcontrol of the coefficient of thermal expansion (CTE). An exemplarycermet 12 may exhibit properties such as high melting temperatures(greater than 1500° C.), high fracture toughness (22 MPa·m^(1/2)), highstrength, high oxidation resistance, controlled porosity (greater than50%), inexpensive starting materials, an ability to be formed into netshapes, electrically conducting, light weight (less than 3 grams/cm³),high heat capacity, and controllable CTE.

Cermet 12 may be made using conventional powder metallurgy techniques.However, an exemplary manufacturing method mixes metallic and ceramicpowders and uses a combustion synthesis process in order to form filter10 in a single step. In this process, a net shape filter 10 can beproduced. In an exemplary embodiment, a mixture is formed of aluminumand transition metal powders mixed together in a 1:1 atomic ratio andalumina powder. A small amount of organic binder, such as one weightpercent polyvinyl alcohol (PVA), may be used. Upon combustion synthesis,cermet 12 is formed having an alumina ceramic phase 16 and an aluminidemetallic phase 18 such as NiAl, CoAl, or FeAl. In another exemplaryembodiment, aluminum and transition metal powders such as nickel,cobalt, or iron powders are mixed in a ratio of 1:3 to form an aluminidemetallic phase 18 such as Ni₃Al, Fe₃Al, or CO₃Al. In another exemplaryembodiment, a sacrificial filler such as polystyrene spheres or fibersmay be added to the mixture to increase formation of pores 14. In allcases, the green body is placed in a structurally configured mold andpressed into discs or cylinders to form a green compact.

The green compact is then fired in a furnace between 600° C.-700° C. orhigher to set off the combustion synthesis process. At 660° C., thealuminum powder melts. The molten aluminum spreads over the surface ofthe transition metal particles by capillary action. Molten aluminumreacts with the transition particles in a highly exothermic reaction toform an aluminide compound. The extremely reactive molten aluminumreacts with the transition metal powder and sets off a solid flame. Thealumina is not involved in the reaction. The solid flame is an intenselyluminous combustion front separating the initial reactant mixture andthe solid combustion product. In a pure metallic combustion synthesisprocess, the combustion front is white-hot and the temperature isextremely high. However, in the exemplary embodiments of the presentinvention, the presence of ceramic phase 16 made from alumina moderatesthe combustion process. The combustion process continues until theentire green compact has been reacted to form a net shape cermet 12 withan aluminide metallic phase 18 and an alumina ceramic phase 16. As anexample, the chemical reaction involved when nickel is used as thetransition metal is shown below.Aluminum combustion synthesis: 3Ni+3Al+Al₂O₃→3NiAl+Al₂O₃  (1)

In another embodiment of the combustion synthesis process, NiAl-aluminacermets may be formed using aluminum particles and thermite (NiO)particles as starting materials. When aluminum reaches the meltingtemperature, it is extremely reactive. The molten aluminum reduces NiOto Ni. During this reduction step, the Al reacts with the oxygen to formalumina, and the remaining molten Al combusts with Ni to form NiAl. Theenergy released by alumina and NiAl formation is tremendous and wouldraise the overall reaction temperature higher than that from thealuminum combustion synthesis process. Net shape bulk products formed bythe aluminum-thermite reaction would thus achieve higher densitiesbecause the reaction temperature is significantly higher than thereaction in the previous embodiment. The chemical reaction for thealuminum-thermite reaction is shown below.Aluminum-thermite combustion synthesis: 5Al+3NiO→3NiAl+Al₂O₃  (2)

If a sacrificial filler is added, it is burned off during this process,assisting in leaving pores 14 behind. The sacrificial filler and thevolume change due to the formation of aluminide metallic phase 18 allcontribute to the formation of pores 14. In an exemplary embodiment,spherical and fiber sacrificial filler materials are used to produce ahighly porous cermet 12 with non-linear pore channels. Consolidationpressure affects porosity development of cermet 12. Higher consolidationpressures lead to a denser, less porous material. Also, the size andshape of the ceramic particles used for ceramic phase 16 control theshape and size of pores 14. Larger ceramic particles lead to a largepore size for pores 14. For example, when the ceramic particle size wasbetween 5-10 μm, the average porosity of pores 14 is less than 10 μm.When the ceramic particle size was between 100-200 μm, the averageporosity is greater than 50 μm. Exemplary materials for the sacrificialfiller are polystyrene particles, Styrofoam® particles, sugar, cornstarch, hair, and organic long, thin fibers. Referring to FIG. 3A, aphotomicrograph of a cross-section of cermet 12 produced with sugarfiller materials is shown. The sizes of pores 14 in FIG. 3A ranged fromsubmicron to 150 μm.

In another exemplary embodiment, hair fibers are frozen in liquidnitrogen and then crushed into short fragments. The hair fibers mix wellwith the metal and ceramic powders and are compacted into the greencompact. The green compact is fired under the conditions previouslydiscussed herein. During combustion synthesis, the hair fibers burn outand produce linear or longitudinal pore channels. These type of poresand channels facilitate good gas and fluid transport through the filterand produce a lower pressure drop across filter 10 during use. Thephotomicrograph in FIG. 3B shows a cross-section of pores 14 producedwith a human hair sacrificial filler. FIG. 3C shows a longitudinalsection of pores 14 produced with a human hair sacrificial filler. It iscurrently believed by the inventor that animal hairs will producesimilar results. The sacrificial filler materials need not be limited tothe examples herein and any suitable combustible materials may be usedin the process as long as they substantially burn off to assist information of pores 14.

Referring to FIGS. 3D-3F, in another exemplary embodiment, a gradedporosity in cermet 12 may be produced during the synthesis process.Relatively smaller sacrificial filler materials produce smaller pores 14while relatively larger sacrificial filler materials produce largerpores 14. Sequential layering of smaller and larger sacrificial fillermaterials in the powder mixture in the mold during the consolidationoperation produces a graded porous cermet 12. Referring to FIG. 3D, theporosity may be graded in the direction from top to bottom of cermet 12.Referring to FIGS. 3E and 3F, the porosity may be graded across thelength of cermet 12. After combustion synthesis, pores 14 of cermet 12will retain layers of pores reminiscent of the sizes of the initialsacrificial filler materials.

Referring to FIGS. 4A-4C, in another exemplary embodiment, reinforcementmaterial 17 can be added to the green compact prior to combustion. FIG.4A is a longitudinal view of cermet 12 synthesized with a metalreinforcement material 17. FIG. 4B is a sectional view of cermet 12synthesized with a metal reinforcement material 17. FIG. 4C is asectional view of cermet 12 reinforced by multiple resistive heatingelements 20. Exemplary structures suitable for use as metalreinforcement 17 include long, thin metal fibers or metal screens whichare incorporated into the green compact prior to consolidation.Exemplary metals suitable for use as reinforcement material 17 includestainless steels, nickel superalloys, cobalt alloys, titanium alloys,and combinations thereof. In another exemplary embodiment, reinforcementmaterial 17 may be ceramic fibers such as alumina, silicon carbide, orsilicon nitride. In an exemplary embodiment, reinforcement material 17may be fused into cermet 12 during the combustion synthesis process.

In another exemplary embodiment of the combustion synthesis process, themanufacturing of filter 10 may be performed under a nitrogen atmosphere.Cermet 12 of filter 10 will emit ammonia after activation by water.FIGS. 5A and 5B show the gas chromatography (GC) analysis of the ammoniastandard and the ammonia generated from a cermet filter afteractivation. PH paper tests further confirmed generation of ammonia fromcermet 12 by turning dark blue after cermet 12 was activated, indicatingthe presence of ammonia. During ammonia emission, cermet 12 generates asignificant amount of heat. The exothermic reaction indicates formationof new phases in cermet 12 during the combustion synthesis reaction.These new phases are currently believed by the inventor to benitrogen-containing nitride compounds that will hydrolyze to give offammonia. It is well known that bulk AlN and Si₃N₄ can be synthesizedfrom metal powder compacts by a high pressure nitrogen combustionprocess. It is currently believed by the inventor that the combustionsynthesis processes can form other metal nitrides. These new phasesformed in cermet 12 are currently believed by the inventor to be sometype of metal nitrides. These nitride phases produce ammonia when theyare activated by water. The ammonia emission phenomenon is also observedwith cermet filters synthesized with sacrificial filler materials suchas sugar. The general combustion synthesis reactions forammonia-producing cermet filters are represented by the chemicalequations below.

${Ni} + {Al} + {{Al}_{2}O_{3}\mspace{14mu}\overset{N_{2}}{\bullet}\mspace{14mu}{NiAl}} + {{Al}_{2}O_{3}} + \Omega$${Ni} + {Al} + {{Al}_{2}O_{3}} + {{sugar}\mspace{20mu}\overset{N_{2}}{\bullet}\mspace{14mu}{NiAl}} + {{Al}_{2}O_{3}} + \Omega$Ω = ammonia-producing  phasesAlternatively, the aluminum-thermite combustion synthesis process may beused instead of the aluminum combustion synthesis process to produce anickel aluminide-alumina cermet having ammonia-producing phases.

In another exemplary embodiment, mixed filler materials, sodiumcarbonate (Na₂CO₃) or sodium bicarbonate and sugar, are used in thecombustion synthesis of cermet 12. Alternatively, any other alkalicarbonates or bicarbonates may be used. When the combustion synthesis iscarried out under a nitrogen atmosphere, ammonia-producing phases andadditional new phases are formed in cermet 12. These additional newphases generate light hydrocarbon gases when cermet 12 is activated bywater. The major hydrocarbon gas produced is methane. However, otherlight hydrocarbon gases have also been detected. FIGS. 6A and 6B showthe GC analysis after activation. The primary hydrocarbon produced ismethane with minor amounts of other higher hydrocarbons. These newadditional phases are currently believed by the inventor to be metalcarbides. Particularly, alkaline carbides such as sodium carbide willproduce light hydrocarbon gases when hydrolyzed. The compositions of theammonia- and hydrocarbon gas-producing phases have not been fullyidentified. This alternative formulation for ammonia- and hydrocarbongas-producing cermet filters is shown in the following chemicalequation.

${Ni} + {Al} + {{Al}_{2}O_{3}} + {sugar} + {{Na}_{2}{CO}_{3}\mspace{14mu}\overset{N_{2}}{\bullet}\mspace{14mu}{NiAl}} + {{Al}_{2}O_{3}} + {{Na}_{2}O} + \Omega + \Phi$Ω = ammonia-producing  phases  Φ = light  hydrocarbon  gas-producing  phasesAlternatively, the aluminum-thermite combustion synthesis process may beused instead of the aluminum combustion synthesis process to produce anickel aluminide-alumina cermet having ammonia-producing phases andhydrocarbon gas-producing phases.

Ammonia and hydrocarbon gases are reducing agents for NO_(x), which ispresent in the diesel exhaust gas. The internal generation capability ofreducing agents has significant implications for destruction of exhaustNO_(x). Further, sodium carbonate (Na₂CO₃) decomposes to CO₂ gas andNa₂O during the combustion synthesis process. If different alkalicarbonates or bicarbonates are used instead of sodium carbonate orbicarbonate, other types of alkali oxides will be formed duringsynthesis of cermet 12. Further, CO₂ escaping from the green compactduring the combustion synthesis process produces pores 14 in cermet 12.

In an exemplary embodiment, post combustion synthesis leaching of cermet12 dissolving the Na₂O particles further increases the porosity ofcermet 12. The leaching may be accomplished by soaking cermet 12 in hotor cold water to dissolve the sodium oxide. In another exemplaryembodiment, the Na₂O is used to absorb NO_(X) during use of filter 10.

In an exemplary embodiment, cermet 12 is electrically conductive so thatdirect internal electrical heating is possible when a current is passedthrough cermet 12. The temperature of cermet 12 is controlled by themagnitude of the applied current. A larger current will yield a highertemperature for cermet 12. As an example, the battery on a vehicle maybe used to provide a DC power source to accomplish this. However,uniform electrical heating depends on good contact and continuitybetween the portions of metallic phase 18 as well as substantialuniformity throughout cermet 12. The electrical resistance of cermet 12may be tailored by adding additional metal powders to the green compact.To increase the electrical resistance of cermet 12, metals such aschromium, manganese, silicon, etc. may be added to the powder mixturebefore combustion.

Referring to FIG. 7, in an exemplary embodiment that uses directinternal electrical heating, electrodes 23 are incorporated into cermet12 during the combustion synthesis process. FIG. 7 shows a thinstainless steel ring electrode 23 that has been bonded to the surface ofcermet 12 during combustion synthesis. An Electrical wire may beattached to the electrode to provide direct internal heating. Duringcompaction, the powder mixture is sandwiched between electrodes 23inside the mold. In an exemplary embodiment, to assist bonding ofelectrodes 23 to cermet 12, nickel and aluminum fine powders may becoated on the underside of the electrodes using silver paint. However,another metal besides nickel may be used depending on the composition ofmetallic phase 18. The combustion synthesis process will result inpermanent bonding of electrodes 23 to cermet 12 in one single operation.

Referring to FIGS. 8A-8C, another exemplary embodiment uses internalresistive heating element 20 incorporated in cermet 12. FIG. 8A shows across-sectional view of cermet 12 containing multiple resistive heatingelements 20. FIG. 8B shows a frontal view of cermet 12. Resistiveheating element 20 may be made from nickel-chromium alloys (nichrome),nickel-chromium-iron alloys, molybdenum disilicide (MoSi₂), or any otherappropriate heating element material known to one of ordinary skill inthe art. In another exemplary embodiment, the coefficient of thermalexpansion of resistive heating element 20 may be selected to besubstantially the same as cermet 12.

During combustion synthesis, resistive heating element 20 will bepermanently bonded inside filter 10. Referring to FIG. 8C, in anotherexemplary embodiment, resistive heating element 20 may be coated withceramic material 21 prior to incorporating it inside filter 10. Examplesof such ceramic materials 21 are refractory oxides such as zirconiumdioxide (ZrO₂), alumina, magnesium oxide (MgO), silicon dioxide (SiO₂),or titanium dioxide (TiO₂). These types of ceramic materials are wellknown to one of ordinary skill in the art. The ceramic material 21 maybe used to electrically insulate resistive heating element 20 to preventstray currents from passing through cermet 12. In another exemplaryembodiment, resistive heating element 20 structurally strengthens cermet12. Referring to FIG. 9, in another exemplary embodiment, filter 10 maybe electrically insulated with insulation 19. An external heating source22 may generally surround filter 10 and insulation 19 to heat filter 10.External heating source 22 may be a source such as a resistance heatingcoil. Other types of external heating sources will be known to one ofordinary skill in the art.

Referring to FIGS. 10A-10B, in another exemplary embodiment, filterhousing 24 is reaction bonded to cermet 12 of filter 10 during thecombustion synthesis process. Exemplary materials for filter housing 24include stainless steels, nickel superalloys, and cobalt alloys. Othermaterials will be known to one of ordinary skill in the art. Prior tocompaction of the metal and ceramic powders of cermet 12, the interiorof filter housing 24 is coated with a thin layer of aluminum and nickelpowder. Another metal besides nickel may be used depending on thecomposition of metallic phase 18. For instance, iron would be suitableif the metallic phase 18 is an iron aluminide. The green cermet powderis then compacted in filter housing 24 with the thin layer of aluminumand nickel powder in place. During combustion synthesis, the aluminumand nickel powder also combusts. The combustion heat from the processin-situ bonds filter 10 permanently to the wall of filter housing 24.FIG. 10B shows good bonding between cermet 12 of filter 10 and filterhousing 24. This exemplary embodiment provides a single-step process toform and bond the cermet 12 of filter 10 to filter housing 24.

Referring to FIG. 11A, filter 10 is coupled to exhaust system 26 ofinternal combustion engine 25 on a vehicle 27, such as a heavy-dutydiesel engine truck. Carbon particles present in exhaust gases 28 willbe trapped by pores 14 (not shown) of filter 10. Filtered exhaust gases30 then exit filter 10 containing substantially less pollutants. Duringengine operation, filter 10 may heat up periodically or maintaincontinuous heating to burn off collected carbon particles and keep pores14 open. For instance, electrical source 34 on vehicle 27 may be used toheat filter 10. Further, the burning off of the carbon particles reducesNO_(X) gases in the final exhaust gas. The carbon particles in theexhaust stream are very fine and have extremely high active surfaces. Atelevated temperatures on a condensable surface such as filter 10, thecarbon particles can destroy NO_(X) and lower the NO_(X) level in thefinal exhaust gas. Further, under an oxidizing environment, cermet 12can destroy CO, H₂, and other hydrocarbon gases. Since intermetallic andoxide compositions have a profound influence on pollutant destruction,the catalytic properties of cermet 12 and the operating environment canbe tailored to oxidize CO and hydrocarbons while also destroying NO_(X).The process by which the NO_(X) gases and carbon particles are destroyedis represented by the following chemical equations:C_((s))+2NO_((g))→N₂ _((g)) +CO₂ _((g))C_((s))+NO₂ _((g)) →½N₂ _((g)) +CO₂ _((g))

In an exemplary embodiment, pores 14 are of sufficient concentration sothat the pressure drop is less than 5 psi across filter 10. Under a fuellean condition, non-transient steady state driving conditions, theamount of carbon particulate generated from a diesel engine may not beenough to reduce all of the NO_(X) present. Thus, referring to FIG. 11B,in another exemplary embodiment using diesel fuel, vapor from theheadspace of the fuel tank 32 can be injected into filter 10 forsupplemental NO_(X) reduction.

The tables below include data from tests of various intermetallic andintermetallic-oxide cermets used for filter 10. The data in thefollowing tables is merely illustrative and other variations on thecompositions of the cermets used are fully embraced by the presentinvention. Tables 1-6 show the test results for several cermet filtercompositions. Table 1 shows nitric oxide (NO) conversion to nitrogen fortwo cermet filters and a molybdenum disilicide filter under a reducingatmosphere. Table 2 shows the percent products of incomplete combustion(PICs) destroyed as a function of temperature for a specific cermetcomposition. Tables 3-7 show the results of catalytic steam reforming ofvarious hydrocarbon fuels to synthesis gas (CO and H₂) by a 50 wt %NiAl-50 wt % alumina cermet filter. Tables 8-9 show pressure drop datawith and without the presence of filtered carbon particles in a 50 wt %NiAl-50 wt % alumina cermet filter having approximately 30% porosity.

Table 10 shows test data that simulated the removal of exhaustgas-entrained fine carbon particles generated from an internalcombustion engine such as a diesel engine. The individual carbon grainsize was approximately 10 nanometers. Agglomerated particle size wasapproximately 0.5-1.0 μm. The carbon particles were generated by thethermal plasma decomposition of methane. An airflow rate of 60liters/minute under high pressure (56 psi) was used. The test lasted 60minutes. The porosity of the cermet filter used in the pressure droptests was approximately 30 percent. Test data shows that for a filterporosity of approximately 30 percent containing approximately 0.448 in²filter area, the carbon filtration efficiency was 99.86 percent. Noclogging of the cermet filter was observed. The weight of the trappedcarbon after filtering was measured by tapping the cermet filter toremove all of the carbon particles.

Although the foregoing description of embodiments and test data containsmany specifics, these should not be construed as limiting the scope ofthe present invention, but merely as providing illustrations of someexemplary embodiments. Similarly, other embodiments of the invention maybe devised which do not depart from the spirit or scope of the presentinvention. The scope of the invention is, therefore, indicated andlimited only by the appended claims and their legal equivalents, ratherthan by the foregoing description. All additions, deletions, andmodifications to the present invention, as disclosed herein, which fallwithin the meaning and scope of the aims are embraced thereby.

TABLE 1 NO_((g)) Reduction for NiAl Cermets and MoSi₂ Under a ReducingAtmosphere Test Condition: 5% NO + 1.67% C₂H₄ + 93.33% He % NO_((g))Conversion to N₂ Under a Reducing Atmosphere 50 wt % NiAl + 50 wt %NiAl + Temperature (° C.) 50 wt % ZrSiO₄ 50 wt % Fe₂O₃ MoSi₂ 300 0 0 0400 0 2.5 0 475 0 2.6 2 550 0 4.7 2 623 3.8 13.3 2 696 11.3 43.1 3 79738.7 98.3 7 904 100

TABLE 2 % Products of Incomplete Combustion Destroyed vs. Temperaturefor a Cermet Composition of (NiAl)_(0.2)/Ni_(0.02)/(ZrSiO₄)_(0.04)Temperature (° C.) C₃H₆ CH₄ CO 25 0 0 0 101 0 0 0 203 2.1 0 5.3 302 1.40 6.1 403 0 0 8.9 478 11.3 15.9 24 553 47.8 233 81.2 627 93.8 25.2 97.0702 100 36.0 100 797 100 52 100

TABLE 3 Steam Reforming of Methanol Using a 50 wt % NiAl-50 wt % Al₂O₃Test Conditions: 10 cc CH₃OH/H₂O = 0.5 mole ratio mixture + 5 cc HeTemperature (° C.) CO₂ (vol. %) H₂ (vol. %) CO (vol. %) 500 0.1 13.0 3.5600 1.5 43.0 11.4 700 4.7 46.0 9.6 800 2.2 47.7 12.0 900 2.1 50.0 15.1967 3.2 50.3 12.4

TABLE 4 Steam Reforming of Unleaded Gasoline Using a 50 wt % NiAl-50 wt% Al₂O₃ Cermet Filter Test Conditions: 6.4 cc gasoline + 12.8 cc H₂O 10cc He Temperature (° C.) CO₂ (vol. %) H₂ (vol. %) CO (vol. %) 788 0.25.7 0.5 896 0.3 4.6 1.2 1018 0.4 5.9 0.4 1034 3.7 22.1 2.2 1042 4.2 24.42.7 1050 3.7 20.2 1.9

TABLE 5 Steam Reforming of a #1 Diesel Fuel Using a 50 wt % NiAl-50 wt %Al₂O₃ Cermet Filter Test Conditions: 6.4 cc Diesel Fuel + 12.8 cc H₂O 10cc He Temperature (° C.) CO₂ (vol. %) H₂ (vol. %) CO (vol. %) 902 0.33.2 3.3 1000 0.3 25.2 9.4

TABLE 6 Steam Reforming of #2 Diesel Fuel Using a 50 wt % NiAl-50 wt %Al₂O₃ Cermet Filter % Conversion = {[CO] + Temperature (° C.)[H₂]}/{[CO] + [H₂] + Σ [C_(x)H_(y)]} 600 43.7 700 48.9 800 53.4 900 59.7968 72.6 1013 94.2

TABLE 7 Steam Reforming of Methane Using a 50 wt % NiAl-50 wt % Al₂O₃Cermet Filter Test Conditions: 5.0 cc CH₄ + 12.8 cc H₂O 35 cc HeTemperature (° C.) CO₂ (vol. %) H₂ (vol. %) CO (vol. %) 703 <0.1 <0.1<0.1 791 <0.1 <0.1 <0.1 905 <0.1 1.3 0.2 1005 <0.1 6.5 1.4

TABLE 8 Pressure Drop Tests without Carbon Particles in a 50 wt %NiAl-50 wt % Al₂O₃ Cermet Filter Temperature Flow rate Line Upstream (°C.) (l/m) P (psi) (psi) Downstream P (psig) 24 10 56 7 0 24 20 56 18 024 30 56 25 0 24 40 56 32 0 24 60 56 47 0

TABLE 9 Pressure Drop Tests with Carbon Particles in a 50 wt % NiAl-50wt % Al₂O₃ Cermet Filter with 30 % Porosity Temperature Flow Line PUpstream (° C.) rate (l/m) (psi) (psi) Downstream P (psig) 24 10 56 8.50 24 20 56 15 0 24 30 56 23 0 24 40 56 30 0 24 50 56 37 0 24 60 56 51.50

TABLE 10 Fine Carbon Particulate Filtration Tests Initial wt of cermetfilter = 3.3073 g Wt of carbon before filtering = 1.3846 g Final wt ofcermet filter = 3.3070 g Wt of carbon after filtering = 1.3826 g Noclogging of the filter observed Carbon filtration efficiency = 99.86%Effective cermet filter area = 0.448 in². Filter porosity ~ 30%

1. A method of producing a structure, the method comprising: forming amixture of transition metal particles, aluminum particles, and ceramicparticles selected from the group consisting of alumina, zirconiasilicate, zirconia, mullite, cordierite, and iron III oxide; pressingthe mixture to form a green compact body; heating the body in anitrogen-containing atmosphere and forming a discontinuous ceramic phasebonded by a metallic phase; and reacting at least a portion of the bodywith nitrogen atoms of the nitrogen-containing atmosphere to form anammonia-emitting phase; and hydrolyzing the body.
 2. The method of claim1 further comprising adding sugar to the mixture.
 3. The method of claim1 further comprising adding an alkali carbonate, an alkali bicarbonate,sugar, or combinations thereof to the mixture.
 4. The method of claim 3further comprising forming the body to contain a hydrocarbon-emittingphase.
 5. The method of claim 3 further comprising forming the body tocontain an alkali oxide phase.
 6. The method of claim 5 furthercomprising dissolving a portion of the alkali oxide phase.
 7. The methodof claim 1 further comprising placing the mixture within a housing priorto heating and reaction bonding the mixture to the housing upon theheating.
 8. The method of claim 1 further comprising adding asacrificial filler to the mixture that substantially burns off duringthe heating of the mixture to increase porosity.
 9. The method of claim1 further comprising providing a resistive heating element disposedwithin the mixture.
 10. The method of claim 9 further comprisingproviding the resistive heating element with a ceramic coating.
 11. Themethod of claim 1 further comprising providing a structuralreinforcement phase disposed within the mixture.
 12. The method of claim1 further comprising providing a structural reinforcement phase disposedwithin the mixture selected from the group consisting of metal fibers,ceramic fibers, and metal screens.
 13. The method of claim 1 furthercomprising providing electrodes integrally bonded with the ceramic andmetallic phases.
 14. The method of claim 1 further comprising formingthe structure to have a substantial number of pores.
 15. The method ofclaim 1 further comprising forming the structure material to have agraded porosity.
 16. A method of producing a structure comprising:forming a mixture of thermite particles and aluminum particles; pressingthe mixture to form a green compact body; heating the body in anitrogen-containing atmosphere and forming a discontinuous ceramic phasebonded by a metallic phase; and reacting at least a portion of the bodywith nitrogen atoms of the nitrogen containing atmosphere to form anammonia-emitting phase; and hydrolyzing the body.
 17. The method ofclaim 16 further comprising adding sugar to the mixture.
 18. The methodof claim 16 further comprising adding an alkali carbonate, an alkalibicarbonate, sugar, or combinations thereof to the mixture.
 19. Themethod of claim 18 further comprising forming the body to contain ahydrocarbon-emitting phase.
 20. The method of claim 18 furthercomprising forming the body to contain an alkali oxide phase.
 21. Themethod of claim 20 further comprising dissolving a portion of the alkalioxide phase.
 22. The method of claim 16 further comprising placing themixture within a housing prior to heating and reaction bonding themixture to the housing upon the heating.
 23. The method of claim 16further comprising adding a sacrificial filler to the mixture thatsubstantially burns off during the heating of the mixture to increaseporosity.
 24. The method of claim 16 further comprising providing aresistive heating element disposed within the mixture.
 25. The method ofclaim 24 further comprising providing the resistive heating element witha ceramic coating.
 26. The method of claim 16 further comprisingproviding a structural reinforcement phase disposed within the mixture.27. The method of claim 16 further comprising providing a structuralreinforcement phase disposed within the mixture selected from the groupconsisting of metal fibers, ceramic fibers, and metal screens.
 28. Themethod of claim 16 further comprising providing electrodes integrallybonded with the ceramic and metallic phases.
 29. The method of claim 16further comprising forming the structure to have a substantial number ofpores.
 30. The method of claim 16 further comprising forming thestructure to have a graded porosity.
 31. A method of producing astructure, the method comprising: forming a mixture of transition metalparticles, aluminum particles, and ceramic particles selected from thegroup consisting of alumina, zirconia silicate, zirconia, mullite,cordierite, and iron IH oxide; pressing the mixture to form a greencompact body; heating the body in a nitrogen-containing atmosphere andforming a discontinuous ceramic phase bonded by a metallic phase; andreacting at least a portion of the body with nitrogen atoms of thenitrogen containing atmosphere to form a hydrocarbon-emitting phase; andhydrolyzing the body.
 32. A method of producing a structure comprising:forming a mixture of thermite particles and aluminum particles; pressingthe mixture to form a green compact body; heating the body in anitrogen-containing atmosphere and forming a discontinuous ceramic phasebonded by a metallic phase; and reacting at least a portion of the bodywith nitrogen atoms of the nitrogen-containing atmosphere to form ahydrocarbon-emitting phase; and hydrolyzing the body.